The present invention relates to a method for use in a telecommunication network, for making an acceptance decision on whether or not to accept an incoming data packet into a buffer, to a controlling device that realizes the method, and to a telecommunication network including such a device.
Today's telecommunication networks such as, e.g. the internet, are fast developing. Traffic is processed as quickly as possible but also the guarantee as to timelines and actual delivery are evolving. With the rapid transformation of the Internet into a commercial infrastructure, demands for different levels of service have rapidly developed. It is becoming apparent that several service classes are necessary each with its own fields of application.
For example, in the header of an Asynchronuous Transfer Mode packet a priority bit is included in order to indicate the kind of priority this packet should receive, a Type of Service byte or a diffserv Code point is included in the header of an Internet packet for indicating the Quality of Service QoS the IP-packet should receive. This is called Differentiated Services.
The loss priority, also called in this document drop priority, or simply priority, of these Differentiated Services are often referred to by a color, e.g., green for packets that should receive the highest priority, called highest loss priority; yellow for packets that should receive the second highest priority and red for packets the should receive the lowest priority, called lowest loss priority.
Differentiated services do not define services per-se, but rather Per Hop Behaviors PHB's. These are intended to allow Internet service providers complete freedom to construct, from PHB's, the intra-domain services they believe will meet their customers' needs. One of the types of mechanism that are known to achieve this type of service is the buffer acceptance mechanism to obtain more stable queues in, e.g., the core routers or edge routers.
Such a method for use in a telecommunication system to generate an acceptance decision during a decision cycle that comprises whether to accept an incoming packet of a data stream in a buffer or not is already known in the art. Indeed, an often used and suitable congestion control mechanism for different routers is called the Random Early Detection mechanism or shortly called Red. This Red mechanism accepts or drops a packet according to the overall average queue length of the buffer, a predefined minimum threshold, a predefined maximum threshold and a predefined maximum drop probability. Red is an active queue management scheme that tries to keep the overall throughput high while maintaining a small average queue length. When the average queue occupancy is below the minimum threshold, no packets are dropped. When the average queue size exceeds the minimum threshold, packets are dropped with an increasing probability. When the average queue size exceeds the maximum threshold, all arriving packets are dropped.
However, in extending RED for service differentiation, i.e., when a large number of drop priorities is used, some disadvantages occur. Indeed, a straightforward implementation of n different drop priorities for such an extended Red mechanism, as well as for some other known buffer acceptance mechanisms, is defining for each drop priority a value for the above mentioned three parameters. One or more parameter values of these three parameters, i.e., minimum threshold, maximum threshold and the drop probability at maximum threshold, differ between the different classes, i.e., drop priorities. In this way, according to an actual value for an average queue length of the buffer, a set of parameters related to a certain drop priority is applied. Indeed, when applying such an extended Red mechanism in, e.g., a fair bandwidth allocation approach, the values of the parameters for the different drop priorities are to be defined such that the minimum threshold of drop priority x, e.g., yellow is bigger than or equal to the maximum threshold that is defined for the drop priority x+1, e.g., red. In this way, all the packets of a data stream of layer x+1 are discarded before starting to drop the packets from layer x. The packets with a higher drop priority value, e.g., value 2 for red, are discriminated from those with a lower drop priority value, e.g. value 1 for yellow.
It has to be highlighted here that the packets with the highest drop priority value, e.g. value x+1 for red, are those packets that receive the lowest priority.
The different steps of such an extended Red mechanism, i.e., a method for use in a telecommunication system to generate an acceptance decision during a decision cycle that comprises whether to accept an incoming packet of a data stream in a buffer or not, are:
determining for a drop priority parameter an actual drop priority parameter value out of the plurality of drop priorities; and
comparing the drop priority with the drop priority of the incoming packet in order to generate the acceptance decision.
In this way, the extended Red mechanism firstly determines according to the actual average queue length of the buffer that is compared to the arranged predefined minimum thresholds and maximum thresholds the associated drop priority parameter, i.e., an actual drop priority parameter value. The drop priority parameter value that is associated with a set of predefined minimum and maximum thresholds between which the actual queue length of the buffer is located provides the actual value for the drop priority parameter. Secondly this actual drop priority parameter value is compared to the drop priority of the incoming packet in order to generate the acceptance decision. The acceptance decision is, according to the above described extended Red mechanism, determined in such a way that the packets with a higher drop priority value as the actual drop priority parameter value are always discarded, and that the packets with a lower drop priority. value as the drop priority parameter value are always accepted, and that the packets with a drop priority equal to the actual drop priority parameter value are dropped with an increasing probability. The drop priority parameter value determines the drop priority class that will be dropped probabilistically.
A problem however, with such an extended Red mechanism as described above and also with other buffer acceptance mechanisms that are defining for each drop priority an additional set of parameters, is that the number of parameters increases linearly as a function of the number of installed drop priorities. Configuration of such a buffer acceptance mechanism becomes complex for, e.g., an operator since it is difficult to define the good values for all these parameters of all the different classes, i.e., too many parameters are to be defined and dimensioned.